1. Field of the Invention
The present invention relates to an electronic control apparatus for electric power steering preferable for use in a vehicle in which an electric motor is used to assist an operation of rotating a steering column.
2. Description of the Related Art
An electric power steering apparatus is provided with an angle sensor for detecting a steering angle of a steering wheel (a rotation angle of a steering column). For example, as described in Japanese Patent Laid-Open No. 2012-103089, the angle sensor operates by power supplied from a battery, and it has a rotation angle sensor for detecting a rotation angle of the rotation shaft of an electric motor, such as a brushless DC motor. The rotation angle sensor refers to an MR sensor or the like which is constituted by magnetoresistive elements for detecting change in the magnetic field of a rotation member constituted by a magnetic body attached to the rotation shaft of the electric motor.
The MR sensor is arranged so that the phase is displaced by π/2 according to a rotation angle of the rotation member, and the magnetoresistive elements the electrical resistance value of which changes according to strength of the magnetic field constitute a bridge circuit. By the angle sensor configured as described above, a controller can acquire an angle signal of a sine wave (sin θ) and a cosine wave (cos θ) corresponding to a rotation angle θ of the electric motor.
Further, as described in Japanese Patent Laid-Open No. 2012-103090, there are known an angle sensor capable of continuing acquiring information related to the steering angle of a steering wheel even under an environment where the ignition switch is not operating, and an electric power steering apparatus steering provided with the angle sensor.
According to the prior-art techniques described above, since it is necessary to provide an angle sensor inside an electric motor, the angle sensor and a controller therefor are separately required. A harness is also necessary to connect the angle sensor and the controller. With increase in the number of parts, measures for noise are also required, which causes increase in cost. Furthermore, when an abnormality occurs in the angle sensor, normal assist control becomes impossible. This is a problem from a viewpoint of reliability.